Geologic hazards

Question 1

Types of landslides

Answer 1

1. Rotational landslide
2. translational landslide
3. block slide
4. rockfall
5. topple
6. earthflow
7. lateral spread
8. debris flow
9. debris avalanche
10. creep

Question 2

is the downslope movement of Earth material , primarily under the influence of gravity. The word landslide is a general term for this and for the landforms created by such movements.

Answer 2

Mass wasting

Question 3

Mass wasting is classified into three sub-categories:

Answer 3

flow, slide, and fall.

Question 4

Individual particles move downslope independently of one another , not as a consolidated mass. Typically occurs in loose, unconsolidated regolith

type of mass wasting

Answer 4

Flow

Question 5

Material Moves as discrete blocks; can occur in regolith or bedrock

type of mass wasting

Answer 5

slide

Question 6

material falls freely in air; typically occurs in bedrock

type of mass wasting

Answer 6

fall

Question 7

subcategory of Flow (4)

Answer 7

Creep
debris flow
earthflow and mudflow
solifluction

Question 8

subcategory of slide (2)

Answer 8

slump
rockslide

Question 9

Slow, visually imperceptible movement

subcategory of flow

Answer 9

creep

Question 10

More than half the particles larger than sand size; rate of movement varies from less than 1m/year to 100km/hr or more

subcategory of flow

Answer 10

debris flow

Question 11

morement of fine-grained particles with large amounts of water

subcategory of flow

Answer 11

earthflow and mudflow

Question 12

Morement of waterlogged soil generally over permafrost

subcategory of flow

Answer 12

solifluction

Question 13

Downward slipping of a block of earth material, usually with a backward rotation on a concave surface

subcategory of slide

Answer 13

slump

Question 14

Usually rapid movement of a newly detached segment of bedrock

subcategory of slide

Answer 14

rockslide

Question 15

Factors that Control Mass Wasting (5)

Answer 15

• Steepness of the slope
• Type of rock and orientation of rock layers
• Nature of consolidated materials
• Water and vegetation
• Earthquakes and volcanoes

Question 16

this is a factor in mass wasting. If frost wedging dislodges a rock from a steep cliff, the rock tumbles to the valley below. However, a similar rock is less likely to roll down a gentle hillside.

Answer 16

Steepness of the slope

Question 17

Imagine a hill underlain by shale, sandstone, and limestone oriented so that their bedding lies parallel to the slope. If the base of the hill is undercut, the upper layers may slide over the weak shale. In contrast, if the rock layers dip at an angle to the hillside, the slope may be stable even if it is undercut. Therefore, a geologist or engineer must consider not only a slope’s stability before construction, but how the project might alter its stability.

Answer 17

Type of rock and orientation of rock layers

Question 18

The angle of repose is the maximum slope or steepness at which loose material remains stable. If the slope becomes steeper than the angle of repose, the material slides.

Answer 18

Nature of consolidated materials

Question 19

To understand how water affects slope stability, think of a sand castle. Even a novice sand-castle builder knows that the sand must be moistened to build steep walls and towers, but too much water causes the walls to collapse. Small amounts of water bind sand grains together because the electrical charges of water molecules attract the grains. However, excess water lubricates the sand and adds weight to a slope.

Answer 19

Water and vegetation

Question 20

An ________ may cause mass wasting by shaking an unstable slope, causing it to slide. A ________ may melt snow and ice near the top of a volcano. The water then soaks into the slope to release a landslide.

Answer 20

Earthquakes and volcanoes

Question 21

Predicting and Avoiding Landslides

Answer 21

Landslides commonly occur on the same slopes as earlier landslides because the geologic conditions that cause mass wasting tend to be constant over a large area and remain constant for long periods of time. Thus, if a hillside has slumped, nearby hills may also be vulnerable to mass wasting.

In addition, landslides and mudflows commonly follow the paths of previous slides and flows.

Awareness and avoidance are the most effective defenses against mass wasting. Geologists construct maps of slope and soil stability by combining data on soil and bedrock stability, slope angle, and history of slope failure in the area. They include evaluations of the probability of a triggering event, such as a volcanic eruption or earthquake. Building codes then regulate or prohibit construction in unstable areas.

Question 22

is a sudden motion or trembling of the Earth caused by the abrupt release of energy that is stored in rocks.
A rock stores elastic energy when it is distorted by a tectonic force. When the rock fractures, it snaps back to its original shape, creating an __________.

Answer 22

Earthquakes

Question 23

is the study of earthquakes and the nature of the Earth’s interior based on evidence from seismic waves.

Answer 23

Seismology

Question 24

Types of Earthquake (2)

Answer 24

Tectonic earthquake
Volcanic Earthquake

Question 25

the energy stored in the crust causes the tectonic plates to move towards, away, or push against each other. With time the stored energy and the movement of the tectonic plates build up the enormous pressure within the region between two plates

Answer 25

Tectonic earthquake

Question 26

Earthquake-related to the volcanic activity are called a ____________. The magnitude of these quakes is usually weak

Answer 26

Volcanic earthquake

Question 27

is a measure of earthquake size and remains unchanged with distance from the earthquake. This is expressed by the Richter Scale.

Answer 27

Magnitude

Question 28

describes the degree of shaking caused by an earthquake at a given place and decreases with distance from the earthquake epicenter . This is expressed by the Mercalli Scale.

Answer 28

Intensity

Question 29

is a logarithmic scale that calculates earthquake size by measuring ground motion on seismographs

Answer 29

Richter Scale

Question 30

earthquakes may cause grains of water-saturated soil to shift closer together, subsequently losing their shear strength and will allow the grains to behave as a fluid.

Answer 30

Liquefaction

Question 31

Earthquake prediction

Answer 31

Long-term earthquake prediction is based on the observation that most earthquakes occur at tectonic plate boundaries.

Short-term prediction is based on occurrences of foreshocks, release of radon gas, changes in the land surface, the water table, electrical conductivity, and erratic animal behavior.

Question 32

Other Geologic Hazards (5)

Answer 32

Volcanic Eruption
Avalanche
Subsidence
Flood
Tsunami

Question 33

iswhen gas and/or lava are released from a volcano —sometimes explosively.

Answer 33

Volcanic Eruption

Question 34

is a rapid flow of snow down a slope, such as a hill or mountain. This can be set off spontaneously, by factors such as increased precipitation or snowpack weakening, or by external means such as humans, other animals, and earthquakes.

Answer 34

avalanche

Question 35

is a general term for downward vertical movement of the Earth’s surface , which can be caused by both natural processes and human activities. This involves little or no horizontal movement, which distinguishes it from slope movement.

Answer 35

Subsidence

Question 36

This occurs in known floodplains when prolonged rainfall over several days, intense rainfall over a short period of time, or a debris jam causes a river or stream to overflow and flood the surrounding area.

When rain falls, the surface runoff can move very quickly from mountainous or hilly areas to low lying areas making these low lying areas more prone to flooding

Answer 36

Flood

Question 37

When an earthquake occurs beneath the sea, part of the sea floor rises or falls. Water is displaced in response to the rock movement, forming a wave. Sea waves produced by an earthquake are called by their Japanese name, ________.

Answer 37

Tsunami